This invention relates generally to hot runner injection molding and more particularly to injection molding apparatus having an improved mold core.
Cooling the mold cores of hot runner injection molding systems to reduce cycle time is well known. Reducing cycle time by even a fraction of a second is very important in large volume applications such as making beverage bottle preforms. As seen in U.S. Pat. No. 5,094,603 to the applicant which issued Mar. 10, 1992, this has normally been done by circulating water or other suitable cooling fluid such as glycol through and around a central cooling tube or pipe in the mold core. While this arrangement is satisfactory from some applications, it would be preferable for many applications if greater cooling efficiency could be achieved.
U.S. Pat. No. 5,498,150 to Check which issued Mar. 12, 1996 does show a mold core having a pipe extending in an outer part with a hemispherical shaped surface at the front end and longitudinally extending grooves therein. While the grooves do increase the cooling surface area, there is still too much delay waiting for the melt to solidify before the mold can be opened for ejection. Furthermore, if the front end of the mold core which forms a part of the cavity is made as thin as possible to achieve greater cooling, it may not have sufficient structural strength to withstand injection pressures of up to 10,000 psi.
Mold-Masters brochure entitled "Introducing Master-Stack Closure Molding Components" shows a mold core having a head with cooling fluid bores extending radially outward therein. While this suitable for molding closures, it is not for molding preforms.